I don’t see the issue, if we say 1 billion is too much (I would choose a lower maximum personally) if their wealth in any way or form is above the max, they have to sell a house or some asset, society in the form of the government (or whathever is in place) take the money to be used for public interest project. It’s really not that punishing, they would literally be the richest people, and they would still have plenty of money/asset to enjoy life. They don’t need more.
There is a difference between productivity and activity, you can be 100% active at work all day, yet 0% productive. Imagine you work on a project for 6 months and then the manager decide to drop the project. You have been unproductive for 6 months, doesn’t mean you were slacking off, but in the end when we calculate the productivity of developers, it is lower because of this.